Stripline devices have found applications in many systems, particularly where extremely high frequency signals are used, i.e. frequencies in the microwave region up to the gigaHertz range. In many such applications, such as stripline resonators, delay lines, filters, and the like, it is desirable that the device be tunable over a reasonable range of resonant frequencies or a reasonable range of propagation velocities. In many applications it is particularly desirable that the technique for tuning the device be such as to maintain the high-Q, or quality factor, thereof over the entire tuning range.
In currently used tuning techniques, stripline resonator devices, for example, use external frequency control circuits utilizing external tunable elements, such as varactors or p-i-n diodes coupled to the resonator device or in the resonator line itself. Such techniques, however, cause a severe deterioration of the quality factor particularly in a device made with superconductive materials so that the desired high-Q requirements of the application cannot be maintained over the tuning range thereof.
Another technique that has been proposed, particularly in superconducting stripline resonators, is to vary the operating temperature of the device. Such an approach, however, has also been found to seriously degrade the Q-factor over the reasonable range involved.
Consequently, it is desirable to devise a technique for tuning a stripline device in such a manner that the required high-Q characteristics thereof are maintained over the frequency range for which the device can be tuned.